1. Field of the Invention
The present invention relates to an intake quantity control apparatus of an internal combustion engine.
2. Description of the Related Art
Known in the art is an intake quantity control apparatus of an internal combustion engine having a variable valve mechanism for controlling a valve opening characteristic of at least one of an intake valve and exhaust valve and having a throttle valve for controlling an intake pressure which is designed to control a quantity of air taken into a combustion chamber (hereinafter referred to as an xe2x80x9cintake quantityxe2x80x9d) by coordinated control of the valve opening characteristic and the opening degree of the throttle valve (more particularly the intake pressure).
In this type of intake quantity control apparatus, changes in characteristics of the valve spring, changes in friction due to fouling, etc. sometimes cause the time lag of the valve opening or valve closing operation with respect to a valve opening or valve closing instruction (operation time lag) to vary among the cylinders or the operation time lag to vary with each intake even in one cylinder. Due to this, sometimes the intake quantity will fluctuate along with time or the intake quantity will fluctuate among cylinders.
Japanese Unexamined Patent Publication (Kokai) No. 2000-204983 discloses as a method for suppressing variation or fluctuation in the intake quantity the method of reducing the opening degree of the throttle valve to cause the intake pressure to drop and thereby lengthen the valve opening time of the intake valve when taking in the same amount of air so as to lower the ratio of the operation time lag with respect to the total valve opening time and thereby reduce its effect.
Incidentally, in the above intake quantity control apparatus, in general a target intake quantity is determined from the operating state of the internal combustion engine, then the valve opening characteristic or intake pressure for realizing this target intake quantity is estimated. In estimation of the valve opening characteristic or intake pressure, a predetermined method is utilized to estimate the valve opening characteristic and intake pressure realizing the target intake quantity and giving the optimum combination of the fuel consumption, emission, torque fluctuation, and other conditions in accordance with the operating state of the internal combustion engine. Further, the thus estimated valve opening characteristic or intake pressure is used as a target control value to control the valve opening characteristic of the intake valve or the exhaust valve or the opening degree of the throttle valve.
However, in practice, due to the above-mentioned time lag or factors in the performance of the variable valve mechanism etc., sometimes the above valve opening characteristic or intake pressure cannot reach the target control value in a predetermined time (for example, control period) or sometimes factors in the mechanism etc. mean the valve opening characteristic or intake pressure cannot reach the target control value.
Further, the valve opening characteristic or intake pressure which ends up being adopted in such cases is sometimes not necessarily optimal in terms of the intake quantity. That is, for example, there is sometimes a valve opening characteristic or intake pressure which can realize the target intake quantity or an intake quantity closer to the target intake quantity in a range of valve opening characteristic or intake pressure realizable in the above predetermined time. That is, in such a case, there is room for controlling the intake quantity more suitably. Japanese Unexamined Patent Publication (Kokai) No. 2000-204983 does not touch upon this problem at all and therefore does not consider it at all.
An object of the present invention is to provide an intake quantity control apparatus of an internal combustion engine able to control the intake quantity more suitably by controlling the valve opening characteristic of at least one of the intake valve and exhaust valve and the intake pressure.
The present invention provides various aspects of intake quantity control apparatuses of internal combustion engines described in the claims as means for achieving this object.
According to a first aspect of the invention, there is provided an intake quantity control apparatus for an internal combustion engine having a valve opening characteristic control means for controlling a valve opening characteristic of at least one of an intake valve and an exhaust valve and an intake pressure control means for controlling an intake pressure and controlling the valve opening characteristic and the intake pressure so as to control the intake quantity, comprising a target intake quantity determining means for determining a target intake quantity for after elapse of a predetermined time, a means for determining a range of the valve opening characteristic realizable in a predetermined time by the valve opening characteristic control means, and a means for determining a range of intake pressure realizable in a predetermined time by the intake pressure control means, the valve opening characteristic and the intake pressure being controlled by the valve opening characteristic control means and the intake pressure control means so as to become a target valve opening characteristic and target intake pressure set in the realizable ranges based on the target intake quantity.
If setting the valve opening characteristic and intake pressure targeted for control, that is, the target valve opening characteristic and target intake pressure, without considering the ranges realizable in the predetermined time, if the set target valve opening characteristic and target intake pressure are not in the above realizable ranges, the intake quantity realized by the valve opening characteristic and intake pressure adopted as a result of the control will sometimes differ considerably from the target intake quantity. Further, in such a case, sometimes the above target intake quantity can be realized or an intake quantity closer to the target intake quantity can be realized if using another valve opening characteristic and intake pressure in the above realizable ranges.
According to the present invention, since the target valve opening characteristic and the target intake pressure are set in ranges realizable in a predetermined time while considering the target intake quantity and valve opening characteristic and intake pressure are controlled to the target valve opening characteristic and target intake pressure, the target valve opening characteristic and target intake pressure not being realized and the intake quantity ending up becoming an unintentional intake quantity is prevented. That is, by suitably setting the target valve opening characteristic and target intake pressure, it is possible to reliably realize control giving the optimal intake quantity in the range realizable in a predetermined time and as a result the intake quantity is more optimally controlled. Note that the xe2x80x9cvalve opening characteristicxe2x80x9d in the present specification means one or more of the valve lift, action angle, and valve opening/closing timing.
According to a second aspect of the invention, there is provided an intake quantity control apparatus of the first aspect of the invention further comprising a means for estimating a valve opening characteristic and intake pressure for realizing the target intake quantity by a predetermined method, wherein when both the valve opening characteristic and intake pressure estimated by the means are in the realizable ranges, the estimated valve opening characteristic and intake pressure are set as the target valve opening characteristic and the target intake pressure, while when at least one of the estimated valve opening characteristic and intake pressure is not in the realizable range, a valve opening characteristic and intake pressure in the realizable ranges whereby the intake quantity becomes closest to the target intake quantity or the intake quantity becomes the target intake quantity are set as the target valve opening characteristic and the target intake pressure.
The valve opening characteristic and intake pressure for the above target intake quantity are for example estimated by a predetermined method so as to find a valve opening characteristic and intake pressure realizing the above target intake quantity and giving the optimal combination of fuel consumption, emission, torque fluctuation, and other conditions in accordance with the operating state of the internal combustion engine. However, the thus estimated valve opening characteristic and intake pressure are not necessarily realizable in the above predetermined time. Further, if making the valve opening characteristic and intake pressure estimated by the above predetermined method the target valve opening characteristic and target intake pressure in such a case, the inconvenience explained with reference to the first aspect of the invention may occur.
According to the present invention, since when at least one of the valve opening characteristic and intake pressure estimated by the predetermined method is not in the above realizable range, the target valve opening characteristic and target intake pressure are set so that the intake quantity becomes closest to the above target intake quantity or the intake quantity becomes the target intake quantity in the realizable ranges, so in the same way as in the first aspect of the invention, it is possible to reliably control the intake quantity to become optimal in the range realizable in the above predetermined time and as a result the intake quantity is more optimally controlled.
According to a third aspect of the invention, there is provided an intake quantity control apparatus of the first aspect of the invention wherein when determining the range of valve opening characteristic realizable in a predetermined time, additional restrictions relating to operation of the internal combustion engine are considered. Even if the valve opening characteristic is realizable in terms of the mechanism and performance of the valve opening characteristic control means, sometimes realization of that valve opening characteristic would not be preferable in terms of operation of the internal combustion engine. According to the present invention, such restrictions can be considered, so it is possible to suppress the occurrence of the various inconveniences which may arise due to intake quantity control.
According to a fourth aspect of the invention, there is provided an intake quantity control apparatus of the third aspect of the invention wherein the additional restrictions relating to operation of the internal combustion engine include a positional relationship and/or valve opening characteristics of the intake and exhaust valves. According to the present invention, it is possible to suppress the occurrence of inconveniences in operation of the internal combustion engine which may arise due to intake quantity control. For example, by including as an additional restriction relating to the operation of the internal combustion engine suppressing the valve overlap to not more than a predetermined amount, it is possible to achieve a reduction in the deposits on the intake valve. Further, by including as an additional restriction relating to the operation of the internal combustion engine keeping the opening position of the intake valve from being delayed from a predetermined position or keeping the closing position of the intake valve from being delayed from a predetermined position, knocking can be suppressed.
According to a fifth aspect of the invention, there is provided an intake quantity control apparatus of the first aspect of the invention wherein when determining the range of intake pressure realizable in a predetermined time, additional restrictions relating to operation of the internal combustion engine are considered. According to a sixth aspect of the invention, there is provided an intake quantity control apparatus of the fifth aspect of the invention wherein the additional restrictions relating to operation of the internal combustion engine include maintaining the intake pressure at not more than a predetermined pressure.
In the fifth and sixth aspects of the invention as well, it is possible to suppress the occurrence of the various inconveniences which may arise due to intake quantity control. In particular, according to the sixth aspect of the invention, as the intake pressure is prevented from becoming higher than the predetermined pressure for the sake of the intake quantity control, when the engine has a configuration to utilize the fact that the intake pressure is a negative pressure, for example, a brake assist mechanism etc., good operation of this configuration can be maintained by suitably setting the above predetermined pressure.
According to a seventh aspect of the invention, there is provided an intake quantity control apparatus for an internal combustion engine controlling an intake quantity by a valve opening characteristic control means for controlling a valve opening characteristic of at least one of an intake valve and an exhaust valve and an intake pressure control means for controlling an intake pressure, comprising a target intake quantity determining means for determining a target intake quantity for after elapse of a predetermined time, a target valve opening characteristic determining means for determining a target valve opening characteristic of the valve opening characteristic control means based on the target intake quantity, a target intake pressure determining means for determining a target intake pressure of the intake pressure control means based on the target intake quantity and the target valve opening characteristic, a means for determining a range of valve opening characteristic realizable in a predetermined time by the valve opening characteristic control means, a means for determining a range of intake pressure realizable in a predetermined time by the intake pressure control means, an operation region determining means determining a realizable operation region from ranges of realizable valve opening characteristic and intake pressure, and a target value resetting means for determining a suitable operation point from the range of operation region when the operation point determined from the target valve opening characteristic and the target intake pressure is not in the realizable operation region and resetting the target values of the valve opening characteristic control means and the intake pressure control means from the operation point.
According to an eighth aspect of the invention, there is provided an intake quantity control apparatus of the seventh aspect of the invention wherein the target value resetting means determines an operation point able to realize the target intake quantity or an intake quantity resembling the target intake quantity in the range of realizable operation region and resets the target values of the valve opening characteristic control means and the intake pressure control means from that operation point.